[media] s5p-fimc: mem2mem driver refactoring and cleanup

Register access functions refactored for camera capture interface
control. Removed the workqueue since it was only useful for FIFO
output mode which is not supported at this time.
Fixed errors on module unload. Comments and whitespace cleanup.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>